1. Field of the Invention
The present inventions pertain to the field of power supplies, and among other things to the regulation of power supplies.
2. Background
Accurate regulation of power supplies is important in many areas. For instance in sensitive electronic devices such as computers and televisions maintaining a constant power supply is important for the operation of the computer or television. Additionally, the advantages of accurate power supply regulation include reduced overall power consumption and reduced damage to equipment by preventing voltage spikes during start up and operation.
Power supplies are regulated by keeping either a current or voltage delivered to a load within a specified range. A power supply is deemed to be in regulation if the load current or voltage is within the specified range and is deemed to be out of regulation if the load current or voltage is outside the specified range.
Problems associated with out of regulation conditions include damage to the load, improper load functioning, and the consumption of power when no power is necessary to operate the load. Therefore, power supplies that regulate output power provided to the load are desired.
A known regulated power supply is depicted in FIG. 1. The regulated power supply of FIG. 1 includes an EMI filter 10 that receives an AC mains voltage. The output of the EMI filter 10 is coupled to rectifier 15 that rectifies the AC mains voltage and then provides the rectified voltage to capacitor 20. Capacitor 20 provides a substantialy DC voltage to a primary winding 25 of transformer 30.
A monolithic power supply control chip 40 includes a MOSFET 45 that is controlled by pulse width modulator 50. When MOSFET 45 is conducting, primary winding 25 has current flowing through it allowing transformer 30 to store energy. When MOSFET 45 is not conducting, the energy stored in the transformer 30 induces a voltage across the secondary winding 55 which is transferred to a load 60 connected at output terminals 65. A capacitor 70 is coupled to secondary winding 55 in order to maintain the voltage that is being supplied to the load 60 when MOSFET 45 is on.
A feedback circuit 75 is coupled to the load 60. The feedback 75 includes a resistor 80, zener diode 85 and an optocoupler 90. A bias winding 95 is magnetically coupled to primary winding 25 and is used to supply power to the output of the optocoupler 90. When the voltage at load 60 is above combination of the reverse bias voltage of zener diode 85 and the forward voltage drop of light emitting diode 100, a current is generated in the phototransistor 105 by light emitting diode 100. The phototransistor 105 current flows from the bias winding 95 to the control terminal 110 of monolithic power supply control chip 40. The current provided to the control terminal 110 of monolithic power supply control chip 40 controls the duty cycle of MOSFET 45. When the control terminal 110 current increases the duty cycle of MOSFET 45 decreases and the amount of current through primary winding 25 decreases. Therefore, the power provided to the load 60 decreases. As the power supplied to the load 60 decreases, the load voltage decreases which in turn reduces the optocoupler 90 current increasing the duty cycle of MOSFET 45. Thus, the output voltage is regulated at a voltage equal to zener 85 reverse breakdown voltage plus the forward drop of LED 100 in an analog closed loop. Resistor 80 controls the gain of the analog loop.
It should be noted that pulse width modulator 50 is switching at some duty cycle to provide power to the feedback circuit 75 even when there is no load connected to the output terminals 65. This will cause power consumption from switching losses occurring at the operating frequency of the MOSFET 45.
The regulated power supply of FIG. 1 is able to maintain the voltage at the load at a reasonably constant level, while reducing voltage transients due to load and line variations. However, the addition of a feedback winding and pulse width modulation controller makes application of the regulated power supply of FIG. 1 expensive for many power suppliers operating at low powers, especially those below five (5) watts. Additionally, the use of analog pulse width modulation feedback control requires compensation circuitry to stabilize the circuit and to prevent oscillations. The compensation circuit limits the bandwidth of the control loop to one (1) or two (2) kilohertz. The Pulse Width Modulated feedback circuit while effective at regulating the voltage still has time periods when the voltage is above and below the desired level, because of the limited bandwidth of the feedback loop which is in the range of one (1) or two (2) kilohertz even though the switching frequency of the MOSFET 45 may be as high as one hundred (100) kilohertz.
It is therefore desired to create a power supply that is cost effective for low power solutions.
It is further desired to create a power supply that utilizes the minimum amount of components possible.
It is additionally desired to create a power supply that can respond quickly to load transients without losing output regulation.
A presently preferred DC to DC converter comprises an energy storage element that receives a first power level and that provides a second power level, a feedback circuit coupled to the energy storage element, and a regulator circuit coupled to the feedback circuit and to the energy storage element. When a feedback signal is above a threshold the regulator circuit is disabled and when the feedback signal is below said threshold level the regulator circuit is enabled.
In another embodiment a power supply comprises a transforming element that transfers energy and is coupled to receive a first power level and a regulator circuit coupled to the transforming element. The regulator circuit controlling input of the first power level to the transforming element. When an output voltage or current of the transforming element is above a threshold level the regulator circuit is disabled and when output voltage or current of the transforming element is below a threshold level the regulator circuit operates.
In yet another embodiment a regulator circuit comprises a feedback input, a switch operating when a control signal is received at its control terminal, an oscillator that provides a duty cycle signal comprising a high state and a low state. The control signal is provided when no feedback signal is provided and the duty cycle signal is in said high state.
In a further embodiment a power supply comprises an energy storage element coupled to receive a first power level and a regulation circuit coupled between the energy storage element and a source of the first power level. The regulation circuit prevents the energy storage element from receiving the first power level when a current or voltage at the input of the energy storage element is at or above a predetermined threshold level.
In an additional embodiment a power supply comprises a transforming element coupled to receive a first power level and a regulation circuit coupled between the transforming element and a source of the first power level. The regulation circuit prevents the transforming element from receiving the first power level when a current or voltage at the input of the transforming element is at or above a predetermined threshold level.
It is an object of an aspect of the present inventions to create a power supply that is accurately regulated with a minimum amount of time spent out of regulation.
It is another object of an aspect of the present inventions to create a power supply that is cost effective for low power solutions.
It is a further object of the present inventions to create a power supply that utilizes the minimum amount of components possible.
It is also an object of the present inventions to create a power supply that is low cost.
This and other objects and aspects of the present inventions are taught, depicted and described in the drawings and the description of the invention contained herein.